Fog-harvesting, an idea that has been around for several years and already in existence in 17 countries, is a technique that captures potable water from fog. Researchers at MIT, working in collaboration with scientists in Chile, have found a way to improve this technology, making potable water more easily attainable in arid countries.

ADVERTISEMENT

Just as some plants and insects in the world’s driest regions have evolved ways to obtain water from the air, fog-harvesting collects tiny airborne droplets of fog. Existing systems, despite being inexpensive, have proved to be inefficient. They generally have filaments and holes that are too large, resulting in the extraction of only about two percent of water available in a mild fog condition.

The new, more efficient system consists of vertical mesh, which harvests the droplets according to three parameters: the size of the filaments in the nets, the size of the wholes between those filaments, and the coating applied to the filaments. As opposed to the old system, this new technique shows that finer mesh could extract ten percent more, according to MIT postdoc Kyoo-Chul Park PhD, MIT alumnus Shreerang Chhatre PhD, graduate student Siddarth Srinivasan, chemical engineering professor Robert Cohen, and mechanical engineering professor Gareth McKinley.

According to Park, "While some of the organisms that harvest fog do so using solid surfaces — such as the carapace of the Namib beetle, native to the Namib desert of southern Africa — permeable mesh structures are much more effective because the wind-blown fog droplets tend to be deflected around solid surfaces. Thus, a woven mesh structure resembling a window screen turns out to be most effective. With the right chemical coating, fog droplets that form on the screen then slide down to be collected at the bottom and are funneled into buckets or tanks."

Chilean investigators have estimated that if just 4 percent of the water contained in the fog could be captured, that would be sufficient to meet all of the water needs of that nation's four northernmost regions, encompassing the entire Atacama Desert area. And with the MIT-designed system, Park points out, 10 percent of the fog moisture in the air passing through the new fog collector system can potentially be captured.

These findings have been published in Langmuir Journal, a publication of the American Chemical Society. The research was supposed by a Samsung scholarship, the MIT-Legatum Center for Entrepreneurship and Development, MIT’s MISTI-Chile program, and the Xerox foundation.